This application claims the benefit of priority under 35 U.S.C. 119 to Japanese Application Serial No. 2000-170962, filed Jun. 7, 2000. The Japanese Serial No. 2000-170962 names the same inventors as this application: Ser. No. 09/876,305, FUEL SUPPLY CONTROL SYSTEM FOR INTERNAL COMBUSTION ENGINE.
The present invention relates to a fuel supply control system for an internal combustion engine having an exhaust gas recirculation mechanism, and more particularly to such a fuel supply control system for controlling a fuel amount to be supplied to the engine in consideration of the case that the exhaust gas recirculation mechanism is deteriorated to cause a deviation of an exhaust gas recirculation amount from a target value.
After the exhaust gas recirculation mechanism is used over a long period of time, there is a possibility that an exhaust gas recirculation passage or an exhaust gas recirculation valve constituting the exhaust gas recirculation mechanism may be clogged to cause a decrease in exhaust gas recirculation amount from a target value, resulting in an increase in a NOx emission amount. Known is a failure determining method including the steps of measuring an intake pressure when opening the exhaust gas recirculation valve and an intake pressure when closing the exhaust gas recirculation valve in the condition where the operating condition of an internal combustion engine is stable, and determining that the exhaust gas recirculation mechanism has failed if the pressure difference between these intake pressures measured above is smaller than a predetermined value (Japanese Patent Laid-open No. Hei 7-180615).
When exhaust gas recirculation is carried out, an intake air amount is reduced. It is known that such a reduction in the intake air amount is corrected by using an EGR correction coefficient for reducing a fuel supply amount according to the exhaust gas recirculation amount to thereby correct the fuel supply amount (Japanese Patent Laid-open No. Hei 7-127494, for example).
When the deterioration of the exhaust gas recirculation mechanism progresses to such a degree that the failure of the mechanism can be surely determined by the conventional failure determining method mentioned above, the exhaust gas recirculation amount is deviated (decreased) from a target value to cause deterioration in exhaust emission characteristics. Further, in the case of correcting the fuel supply amount by using the EGR correction coefficient as mentioned above, the following problem occurs. That is, in spite of the fact that the actual exhaust gas recirculation amount is decreased from a target value with the progress of deterioration of the exhaust gas recirculation mechanism, the EGR correction coefficient is calculated on the assumption that exhaust gas recirculation corresponding to the target value is executed. As a result, the correction by the EGR correction coefficient becomes excessive (the air-fuel ratio becomes leaner than a desired value), causing increase in the NOx emission amount.
Furthermore, the deterioration in exhaust emission characteristics due to such excessive correction becomes apparent before the degree of deterioration of the exhaust gas recirculation mechanism reaches such a degree that the failure of the mechanism can be surely determined. It is therefore desired to accurately determine the deterioration of the exhaust gas recirculation mechanism, of such a degree that the mechanism has not apparently failed.
It is accordingly a first object of the present invention to provide a fuel supply control system which can more properly perform the correction of a fuel supply amount in consideration of the deterioration of the exhaust gas recirculation mechanism to thereby maintain good exhaust emission characteristics over a long period of time.
It is a second object of the present invention to provide a fuel supply control system having a function capable of accurately determining the deterioration of the exhaust gas recirculation mechanism, of such a degree that the mechanism has not apparently failed.
In accordance with an aspect of the present invention, there is provided a fuel supply control system for controlling a fuel amount to be supplied to an internal combustion engine having an exhaust gas recirculation mechanism comprising an exhaust gas recirculation passage connected between an intake pipe and an exhaust pipe, and an exhaust gas recirculation valve provided in the exhaust gas recirculation passage. The fuel supply control system includes: an intake pressure sensor for detecting an intake pressure (PBA) of the engine; and correcting means for correcting the fuel amount (TOUT) to be supplied to the engine according to a pressure difference (DPBEGR) between an intake pressure detected when opening the exhaust gas recirculation valve and an intake pressure detected when closing the exhaust gas recirculation valve.
With this configuration, the fuel amount to be supplied to the engine is corrected according to the pressure difference (DPBEGR) between the intake pressure when opening the exhaust gas recirculation valve and the intake pressure when closing the exhaust gas recirculation valve. The pressure difference (DPBEGR) decreases as the degree of deterioration of the exhaust gas recirculation mechanism increases. Accordingly, by increasing the fuel supply amount with a decrease in the pressure difference (DPBEGR), the fuel supply amount can be corrected to a proper value according to the degree of deterioration, to thereby maintain good exhaust emission characteristics over a long period of time.
Preferably, the correcting means corrects the fuel amount so that the fuel amount increases with a decrease in the pressure difference.
Preferably, the correcting means measures the pressure difference when the fuel supply to the engine is interrupted.
Preferably, the fuel supply control system further includes an engine rotational speed sensor for detecting a rotational speed (NE) of the engine. The correcting means corrects the pressure difference according to the detected rotational speed of the engine, and corrects the fuel amount according to the corrected pressure difference.
Preferably, the fuel supply control system further includes an air-fuel ratio sensor provided in the exhaust pipe; air-fuel ratio correcting means for calculating an air-fuel ratio correction coefficient (KO2) according to an output from the air-fuel ratio sensor and correcting the fuel amount by using the calculated air-fuel ratio correction coefficient; and deterioration determining means for determining deterioration of the exhaust gas recirculation mechanism according to a difference (DKO2) between the air-fuel ratio correction coefficient calculated during a period of opening the exhaust gas recirculation valve and the air-fuel ratio correction coefficient calculated during a period of closing the exhaust gas recirculation valve. The correcting means corrects the fuel amount when the deterioration determining means determines that the exhaust gas recirculation mechanism is deteriorated.
Preferably, the deterioration determining means comprises means for calculating a first average (KO2WTEGR) of the air-fuel ratio correction coefficient during opening of the exhaust gas recirculation valve and means for calculating a second average (KO2WOEGR) of the air-fuel ratio correction coefficient during closing of the exhaust gas recirculation valve, and calculates the difference (DKO2) by using the first and second averages.
In accordance with another aspect of the present invention, there is provided a fuel supply control system for controlling a fuel amount to be supplied to an internal combustion engine having an exhaust gas recirculation mechanism comprising an exhaust gas recirculation passage connected between an intake pipe and an exhaust pipe, and an exhaust gas recirculation valve provided in relation to the exhaust gas recirculation passage. The fuel supply control system comprises: an air-fuel ratio sensor provided in the exhaust pipe; air-fuel ratio correcting means for calculating an air-fuel ratio correction coefficient (KO2) according to an output from the air-fuel ratio sensor and correcting the fuel amount by using the calculated air-fuel ratio correction coefficient; and deterioration determining means for determining deterioration of the exhaust gas recirculation mechanism according to a difference (DKO2) between the air-fuel ratio correction coefficient calculated during a period of opening the exhaust gas recirculation valve and the air-fuel ratio correction coefficient calculated during a period of closing the exhaust gas recirculation valve.
With this configuration, the deterioration of the exhaust gas recirculation mechanism is determined according to the difference (DKO2) between the air-fuel ratio correction coefficient calculated during the period of opening the exhaust gas recirculation valve and the air-fuel ratio correction coefficient calculated during the period of closing the exhaust gas recirculation valve. When the air-fuel ratio deviates from a desired value to a lean region, the value of the air-fuel ratio correction coefficient (KO2) increases. Therefore, the absolute value of the difference (DKO2) increases as the degree of deterioration of the exhaust gas recirculation mechanism increases. Accordingly, by determining the degree of deterioration according to the difference (DKO2), the deterioration of the exhaust gas recirculation mechanism, of such a degree that the mechanism has not apparently failed can be accurately determined.
Preferably, the fuel supply control system further comprises correcting means for correcting the fuel amount according to a degree of deterioration of the exhaust gas recirculation mechanism when the difference (DKO2) becomes greater than a predetermined value (DKO2EGRF).
Preferably, the fuel supply control system further comprises an intake pressure sensor for detecting an intake pressure of the engine. The correcting means uses a pressure difference (DPBEGR) between an intake pressure detected when opening the exhaust gas recirculation valve and an intake pressure detected when closing the exhaust gas recirculation valve, as a parameter indicating the degree of deterioration of the exhaust gas recirculation mechanism.